C.J. Lister

Yrast decays in 87,89Zr, 87,88,89,90Y and 86Sr from 74,76Ge(18O,xn,yp,zαγ) reactions

Gamma-ray data from 74,76Ge+18O fusion-evaporation reactions are analysed to provide data on yrast decay schemes in 87,89Zr, 87,88,89,90Y and 86Sr. The data include excitation functions, angular distributions, gamma - gamma coincidences, linear polarisation measurements and lifetimes deduced from both Doppler shift attenuation and recoil distance measurements. Shell-model calculations are presented for 88,90Y and 86Sr.

New isotopeY80, and the decays ofSr79,Y81, andY82

The helium-jet recoil transfer technique has been used to study the decays of /sup 79/Sr, /sup 80/Y, /sup 81/Y, and /sup 82/Y, produced by /sup 58/Ni(/sup 24/Mg,2pn), /sup 58/Ni(/sup 24/Mg,pn), /sup 58/Ni(/sup 25/Mg,pn), and /sup 60/Ni(/sup 24/Mg,pn) reactions, respectively. Decay properties of these four radioactivities have been deduced from the analysis of extensive singles and multiparameter spectroscopic measurements. The low lying level structure of /sup 80/Sr, as revealed by the decay of /sup 80/Y, can be reproduced through calculations of the interacting-boson-approximation model which place /sup 80/Sr at or near the O(6) limit. Positron end-point measurements (deduced from (..beta..,..gamma..) coincidence studies) have been used to determine decay energies for each of these nuclides. Nuclidic mass excesses inferred from these data show progressively larger deviations from the predictions of currently available mass models for the more neutron-deficient Y isotopes as the N = Z line is approached. It is suggested that this may reflect the influence of nuclear deformation of these isotopes on the mass surface in the vicinity of N = Z = 40.

High spin single particle states in Er 1 5 2 , 1 5 3

A spectroscopic investigation of yrast and near-yrast states in /sup 152/Er and /sup 153/Er is presented. We report measurements of prompt and delayed excitation functions, ..gamma..-..gamma.. coincidences, isomeric lifetimes, and ..gamma..-ray angular distribution, obtained chiefly from the reactions /sup 144/Sm(/sup 12/C,xn)/sup 152,153/Er using carbon beams of laboratory energy 65--95 MeV. The levels observed extend to a spin of J> or =43/2 and include two long-lived isomers in /sup 153/Er. The nuclear structure is discussed in terms of the shell model and compared with the systematic behavior of levels in N=84 and N=85 isotones.

High spin single-particle states in /sup 152,153/Er

A spectroscopic investigation of yrast and near-yrast states in /sup 152/Er and /sup 153/Er is presented. We report measurements of prompt and delayed excitation functions, ..gamma..-..gamma.. coincidences, isomeric lifetimes, and ..gamma..-ray angular distribution, obtained chiefly from the reactions /sup 144/Sm(/sup 12/C,xn)/sup 152,153/Er using carbon beams of laboratory energy 65--95 MeV. The levels observed extend to a spin of J> or =43/2 and include two long-lived isomers in /sup 153/Er. The nuclear structure is discussed in terms of the shell model and compared with the systematic behavior of levels in N=84 and N=85 isotones.